Encapsulated liquid crystal and method

ABSTRACT

Briefly, according to one aspect of the invention, liquid crystal material, and especially nematic material, is encapsulated; according to another aspect the encapsulated liquid crystal material is used in liquid crystal devices, such as relatively large size visual display devices; and according to further aspects there are provided methods for encapsulating liquid crystal material and for making a liquid crystal device using such encapsulated liquid crystal material.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of my copending, commonlyassigned, U.S. patent application Ser. No. 302,780, filed Sept. 16,1981, now U.S. Pat. No. 4,435,047, issued Mar. 6, 1984, for"Encapsulated Liquid Crystal and Method", the entire disclosure of whichis hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates generally to liquid crystals and, moreparticularly, to encapsulated liquid crystals. Moreover, the inventionrelates to devices using such encapsulated liquid crystals and tomethods of making such encapsulated liquid crystals and devices.

BACKGROUND

Liquid crystals currently are used in a wide variety of devices,including optical devices such as visual displays. Such devices usuallyrequire relatively low power and have a satisfactory response time,provide reasonable contrast, and are relatively economical. The propertyof liquid crystals enabling use, for example, in visual displays, is theability of liquid crystals to transmit light on one hand, and to scatterand/or absorb light, on the other, depending on the alignment (or lackof alignment) of the liquid crystal structure with, e.g. an electricfield applied across the liquid crystal material. An example ofelectrically responsive liquid crystal material and use thereof isprovided in U.S. Pat. No. 3,322,485.

Certain liquid crystal material is responsive to temperature, changingoptical characteristics in response to temperature of the liquid crystalmaterial.

The invention of the present application is disclosed hereinafterparticularly with reference to the use of liquid crystal material thatis particularly responsive to an electric field.

Currently there are three categories of liquid crystal materials, namelycholesteric, nematic and smectic types. The invention of the presentapplication relates in the preferred embodiment described below to useof liquid crystal material which is operationally nematic (ashereinafter defined). However, various principles of the invention maybe employed with various one or ones of the other known types of liquidcrystal material or combinations thereof. The various characteristics ofthe cholesteric, nematic and smectic types of liquid crystal materialare described in the prior art. One known characteristic of liquidcrystal material is that of reversibility; in particular it is notedhere that nematic liquid crystal material is known to be reversible, butcholesteric material is not reversible. One characteristic of areversible material is that the liquid crystal structure will return toits original configuration after an electric field has been applied andthen removed.

To enhance contrast and possibly other properties of liquid crystalmaterial, pleochroic dyes have been mixed with the liquid crystalmaterial to form a solution therewith. The molecules of the pleochroicdye generally align with the molecules of the liquid crystal material.Therefore, such pleochroic dyes will tend to function optically in amanner similar to that of the liquid crystal material in response to achanging parameter, such as application or non-application of anelectric field. Examples of the use of pleochroic dyes with liquidcrystal material are described in U.S. Pat. Nos. 3,499,702 and3,551,026.

An important characteristic of liquid crystal material is anisotropy. Ananisotropic material has different physical properties in differentdirections. For example, liquid crystals are optically anisotropic i.e.they have indices of refraction which vary with the direction ofpropagation and polarization of the incident light.

Liquid crystal material also has electrical anisotropy. For example, thedielectric constant for nematic liquid crystal material may be one valuewhen the molecules in the liquid crystal structure are parallel to theelectric field and may have a different value when the molecules in theliquid crystal structure are aligned perpendicular to an electric field.Since such dielectric value is a function of alignment, for example,reference to the same as a "dielectric coefficient" may be more apt thanthe usual "dielectric constant" label. Similar properties are true forother types of liquid crystals.

Some brief discussion of the encapsulation of cholesteric liquid crystalmaterial is presented in U.S. Pat. Nos. 3,720,623, 3,341,466, and2,800,457, the latter two patents being referred to in the first namedpatent.

In the past, devices using liquid crystals, such as visual displaydevices or other devices, have been of relatively small size. Large sizedevices using liquid crystals, such as, for example, a billboard displayor a sign have not been satisfactorily fabricatable for a number ofreasons. One reason is the fluidity of the liquid crystals, (the liquidcrystal material may tend to flow creating areas of the display thathave different thicknesses). As a result, the optical characteristics ofthe display may lack uniformity, have varying contrast characteristicsat different portions of the display, etc; the thickness variations inturn cause variations or gradations in optical properties of the liquidcrystal device. Moreover, the varying thickness of the liquid crystallayer will cause corresponding variations in the electrical propertiesof the liquid crystal layer, such as capacitance and impendance, furtherreducing uniformity of a large size liquid crystal device. The varyingelectrical properties of the liquid crystal layer, then, also may causea corresponding variation in the effective electric field applied acrossthe liquid crystal material and/or in response to a constant electricfield would respond differently at areas of the liquid crystal that areof different thicknesses.

A pleochroic display, i.e. one in which pleochroic dye and liquidcrystal material are in solution together, has the advantage of notrequiring the use of a polarizer. However, such a pleochroic device hasa disadvantage of relatively low contrast when only nematic liquidcrystal material is used. It was discovered in the past, though, that acholesteric liquid crystal material could be added to the nematic onetogether with the dye to improve the contrast ratio. See White et alarticle, "Journal of Applied Physics", Volume 45, No. 11, November 1974,at pages 4718-4723, for example. The cholesteric material would tend notto return to its original zero field form when the electric field isremoved.

Another problem encountered with pleochroic dye included in solutionwith liquid crystal material, regardless of the particular type ofliquid crystal material, is that the light absorption of the dye is notzero in the "field-on" condition; rather such absorption in the"field-on" condition follows a so-called ordering parameter, whichrelates to or is a function of the relative alignment of the dyes. Theoptical transmission characteristic of liquid crystal material is anexponential function of the thickness of the liquid crystal material;specifically, the "on" state or "field-on" or "energized" state of theliquid crystal material is an exponential function of the thickness ofthe liquid crystal material, and the "absorbing" state or "off" statealso is a different exponential function of the thickness.

To overcome those problems described in the two immediately precedingparagraphs, the liquid crystal material should have an optimum uniformthickness. (As used herein the term "liquid crystal" material means theliquid crystals themselves and, depending on context, the pleochroic dyein solution therewith). There also should be an optimum spacing of theelectrodes by which the electric field is applied to the liquid crystalmaterial. To maintain such optimum thickness and spacing, rather closetolerances must be maintained. To maintain close tolerances, there is alimit as to the size of the device uusing such liquid crystals, for itis quite difficult to maintain close tolerances over large surfaceareas, for example.

BRIEF SUMMARY OF THE INVENTION

Briefly, according to one aspect of the invention, liquid crystalmaterial is encapsulated; according to another aspect the encapsulatedliquid crystal material is used in liquid crystal devices, such asrelatively large size visual display devices and optical shutters; andaccording to further aspects there are provided methods forencapsulating liquid crystal material and for making a liquid crystaldevice using such encapsulated liquid crystal material.

Some terms used herein generally are defined as follows: "liquid crystalmaterial" broadly refers to any type of liquid crystal material thatwill work in the context of the present invention, but preferably refersto operationally nematic liquid crystal material. By "operationallynematic" is meant that, in the absence of external fields, structuraldistortion of the liquid crystal is dominated by the orientation of theliquid crystal at its boundaries rather than by bulk effects, such asvery strong twists (as in cholesteric material) or layering (as insmectic material). Thus, for example, chiral ingredients which induce atendency to twist but cannot overcome the effects of boundary alignmentwould still be considered operationally nematic. Such operationallynematic liquid crystal material may include pleochroic dyes, chiralcompounds, or other co-ingredients. A capsule refers to a containmentdevice or medium that confines a quantity of liquid crystal material,and "encapsulating medium" or "material" is that medium or material ofwhich such capsules are formed. An "encapsulated liquid crystal" or"encapsulated liquid crystal material" means a quantity of liquidcrystal material confined or contained in discrete volumes within theencapsulating medium, for example in a solid medium as individualcapsules or dried stable emulsions.

Capsules according to this invention generally have an approximatelyspherical configuration (though this is not, per se, a requisite of theinvention) having a diameter from about 0.3 to 100 microns, preferably0.1 to 30 microns, especially 3 to 15 microns, for example 5 to 15microns. In the context of this invention, encapsulation and like termsrefer not only to the formation of such articles as are generallyreferred to as capsules, but also to the formation of stable emulsionsor dispersions of the liquid crystal material in an agent (anencapsulating medium) which results in the formation of stable,preferably approximately uniformly sized, particles in a uniformsurrounding medium. Techniques for encapsulation, generally referred toas microencapsulation because of the capsule size, as well known in theart (see, e.g., "Microcapsule Processing and Technology" by Asaji Kondo,published by Marcel Dekker, Inc.) and it will be possible for oneskilled in the art, having regard to the disclosure herein, to determinesuitable encapsulating agents and methods for liquid crystal materials.

A liquid crystal device is a device formed of liquid crystal material.In the present invention such devices are formed of encapsulated liquidcrystals capable of providing a function of the type typically inuringto liquid crystal material; for example, such a liquid crystal devicemay be a visual display or an optical shutter that in response toapplication and removal of an electric field effects a selectedattenuation of optical radiation, preferably including from far infraredthrough ultraviolet wavelengths.

One method of making encapsulated liquid crystals includes mixingtogether liquid crystal material and an encapsulating medium in whichthe liquid crystal material will not dissolve and permitting formationof discrete capsules containing the liquid crystal material.

A method of making a liquid crystal device including such encapsulatedliquid crystal includes, for example applying such encapsulated liquidcrystal material to a substrate. Moreover, such method may includeproviding means for applying an electric field to the liquid crystalmaterial to affect a property thereof.

According to another feature of the invention an operationally nematicmaterial in which is dissolved a pleochroic dye is placed in a generallyspherical capsule. In the absence of an electric field, the capsule walldistorts the liquid crystal structure so it and the dye will tend toabsorb light regardless of its polarization direction. When a suitableelectric field is applied across such a capsule, for example across anaxis thereof, the liquid crystal material will tend to align parallel tosuch field causing the absorption characteristic of such material to bereduced to one assumed when the liquid crystal material is in the planarconfiguration. To help assure that adequate electric field is appliedacross the liquid crystal material in the capsule, and not just acrossor through the encapsulating medium, and, in fact, with a minimumvoltage drop across the wall thickness of the respective capsules, theencapsulating material preferably has a dielectric constant no less thanthe lower dielectric constant of the liquid crystal material, on the onehand, and a relatively large impedance, on the other hand. Ideally, thedielectric constant of the encapsulating medium should be close to thehigher dielectric constant of the liquid crystal.

Contrast of a liquid crystal device employing encapsulated liquidcrystals may be improved by selecting an encapsulating medium that hasan index of refraction that is matched to the ordinary index ofrefraction of the liquid crystal material (i.e. the index of refractionparallel to the optical axis of the crystal. See, e.g. "Optics" by Born& Wolf, or "Crystals and the Polarizing Microscope" by Hartshorne &Stewart. The encapsulating medium may be used not only to encapsulateliquid crystal material but also to adhere the capsules to a substratefor support thereon. Alternatively, a further binding medium may be usedto hold the liquid crystal capsules relative to a substrate. In thelatter case, though, preferrably the additional binding medium has anindex of refraction which is matched to that of the encapsulating mediumfor maintaining the improved contrast characteristic described above.Because the index of refraction of a material is generallystrain-dependent, and strain may be induced in, e.g. the encapsulatingmedium, it may be necessary to consider this effect in matching theindices of refraction of the liquid crystal, encapsulating medium, andbinding medium, if present. Further, if iridescence is to be avoided, itmay be desirable to match the indices of refraction over a range ofwavelengths to the extent possible, rather than at just one wavelength.

A feature of the spherical or otherwise curvilinear surfaced capsulewhich confines the liquid crystal material therein in accordance withthe present invention is that the liquid crystal material tends tofollow the curvature or otherwise to align itself generally parallelwith the curved surfaces of such capsule. Accordingly, the liquidcrystal structure tends to be forced or distorted to a specific form,being folded back on itself in a sense as it follows the capsule wall,so that the resulting optical characteristic of a given capsulecontaining liquid crystal material is such that substantially all lightdelivered thereto will be affected, for example, scattered (when nopleochroic dye is present) or absorbed (when pleochronic dye ispresent), when no electric field is applied, regardless of thepolarization direction of the incident light. Even without dye thiseffect can cause scattering and thus opacity.

Another feature is the ability to control the effective thickness of theliquid crystal material contained in a capsule by controlling theinternal diameter of such capsule. Such diameter control may be effectedby a size fractionation separation process during the making of theencapsulated liquid crystals using any one of a variety of conventionalor novel sorting techniques as well as by controlling the mixingprocess, the quantities of ingredients, and/or the nature of theingredients provided during mixing. By controlling such thicknessparameter to relatively close tolerances, then, the subsequent tolerancerequirements when the final liquid crystal device is made using theencapsulated liquid crystals will not be as critical as was required inthe past for non-encapsulated devices.

Moreover, a further and very significant feature of the presentinvention is that there appears to be no limitation on the size of ahigh quality liquid crystal device that can be made using theencapsulated liquid crystals in accordance with the present invention.More specifically, by providing for confinement of discrete quantitiesof liquid crystal material, for example, in the described capsules, thevarious problems encountered in the past that prevented the use ofliquid crystal material in large size devices are overcome, for eachindividual capsule in effect can still operate as an independent liquidcrystal device. Moreover, each capsule preferably has physicalproperties enabling it to be mounted in virtually any environmentincluding one containing a plurality of further such liquid crystalcapsules mounted to a substrate or otherwise supported for use inresponse to application and removal of some type of excitation source,such as, for example, an electric or magnetic field. This feature alsoenables placement of the liquid crystal material on only selected areasof the optical device, such as in large size displays (e.g. billboards),optical shutters, etc.

Important considerations in accordance with the invention, and thediscovery of the inventor, are that an encapsulating medium havingelectrical properties matched in a prescribed way to the electricalproperties of liquid crystal material encapsulated thereby andadditionally preferably optically matched to optical properties of suchliquid crystal material permits efficient and high quality functioningof the liquid crystal material in response to excitation ornon-excitation by an external source; and that the interaction of theencapsulating medium with the liquid crystal material distorts thelatter in a prescribed manner changing an operational mode of liquidcrystal material. Regarding the latter, by forcing the liquid crystalstructure to distort into generally parallel or conforming alignmentwith the capsule wall, the liquid crystals will absorb or block, ratherthan transmit, light when not subject to an electric field and will befunctional with respect to all manners of incident light regardless ofthe direction of polarization, if any, of such incident light.

With the foregoing in mind, a primary object of the invention is toenable the use of liquid crystal material over relatively largesurfaces, and especially to effect the same while maintaining relativelyhigh quality of operation, controlled uniformity of output andsatisfactory contrast, which is achieved by the encapsulation of thatmaterial.

Another primary object is to confine liquid crystal material whilemaintaining the optical characteristics of such material, and especiallyto effect the same while also maintaining electrical responsiveness ofthe liquid crystal material.

These and other objects and advantages of the present invention willbecome more apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described in thespecification and particularly pointed out in the claims, the followingdescription and the annexed drawing setting forth in detail a certainillustrative embodiment of the invention, this being indicative,however, of but one of the various ways in which the principles of theinvention may be suitably employed.

BRIEF DESCRIPTION OF THE DRAWING

In the annexed drawing:

FIG. 1 is a schematic representation of a prior art liquid crystaldevice;

FIG. 2 is a schematic representation of a liquid crystal device inaccordance with the present invention;

FIG. 3 is an isometric view of a liquid crystal display device inaccordance with the present invention;

FIG. 4 is an enlarged fragmentary view, partly broken away, of a portionof the liquid crystal display device of FIG. 3;

FIG. 5 is an enlarged schematic illustration of a liquid crystal capsulein accordance with the present invention under a no field condition;

FIG. 6 is a view similar to FIG. 5 under an applied electric fieldcondition; and

FIG. 7 is a schematic electric circuit diagram representation of thecapsule with an applied field.

SUMMARY OF A PRIOR ART LIQUID CRYSTAL DEVICE

Referring now in detail to the drawing, wherein like reference numeralsdesignate like parts in the several figures, and initially in FIG. 1, aprior art liquid crystal device is generally indicated at 1. Such device1 includes liquid crystal material 2 sandwiched between electrodes 3 of,for example, indium tin oxide that are deposited for support onrespective mounting or confining substrates 4, such as glass, plasticsheets or the like. The sheets 4 may be clear as may be the electrodes 3so that the device 1 is an optical transmission control device, therebyincident light may be absorbed and/or scattered when no electric fieldis applied by the electrodes 3 across a liquid crystal material 2 andthe incident light may be transmitted through the liquid crystalmaterial 2 when an electric field is applied thereacross. Electric leads5 and switch 6 selectively couple voltage source 7 across the electrodes3 to provide such electric field. The voltage source 7 may be either anAC or a DC voltage source.

The liquid crystal material 2 in the device 1 is somewhat confined bythe substrates 4 for retention in a desired location, say for example,to be used overall as part of a digital display device. On the otherhand, the liquid crystal material 2 must have adequate freedom ofmovement so that it may assume either a random orientation ordistribution when no electric field is applied or a prescribeddistributional or orientational alignment when an electric field isapplied across the electrodes 3. If desired, one of the substrates 4 maybe reflective to reflect incident light received through the liquidcrystal material 2 back through the latter for delivery through theother substrate 4 for subsequent use. The various principles ofoperation and features and disadvantages of the liquid crystal device 1are summarized above and are described in the prior art literature.

The liquid crystal material 2 may be of virtually any type that isresponsive to an electric field applied thereacross so as to have adesired operating characteristic intended for the device 1; the liquidcrystal material 2 also may include, if desired, pleochroic dye materialin solution therewith.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to FIG. 2, an improved liquid crystal device in accordancewith the present invention is indicated at 10. The device 10 includes anencapsulated liquid crystal 11 which is supported by a mountingsubstrate 12 across which an electric field may be applied viaelectrodes 13, 14.

The electrode 13 may be, for example, a quantity of vacuum depositedindium tin oxide applied to the substrate 12, and the electrode 14 maybe, for example, electrically conductive ink. A protective layer orcoating 15 may be applied over the electrode 14 for protective purposesbut such layer 15 ordinarily would not be necessary for supporting orconfining the encapsulated liquid crystal 11 or the electrode 14.Voltage may be applied to the electrodes 13, 14 from an AC or DC voltagesource 16, selectively closable switch 17, and electrical leads 18, 19in turn to apply an electric field across the encapsulated liquidcrystal 11 when the switch 17 is closed.

The encapsulated liquid crystal 11 includes liquid crystal material 20contained within the confines or interior volume 21 of a capsule 22.According to the preferred embodiment and the best mode of the presentinvention, the capsule 22 is generally spherical. However, theprinciples of the invention would apply when the capsule 22 is of ashape other than spherical. Such shape should provide the desiredoptical and electrical characteristics that will satisfactorily coexistwith the optical characteristics of the liquid crystal 20, e.g. index ofrefraction, and will permit an adequate portion of the electric field tooccur across the liquid crystal material 20 itself for effecting desiredalignment of the liquid crystal structure when it is desired to have afield on condition. A particular advantage to the preferred sphericalconfiguration of the capsule 22 will be described below with respect tothe distortion it effects on the liquid crystal structure.

The mounting substrate 12 and the electrodes 13, 14 as well as theprotective coating 15 may be optically transmissive so that the liquidcrystal device 10 is capable of controlling transmission of lighttherethrough in response to whether or not an electric field is appliedacross the electrodes 13, 14 and, thus, across the encapsulated liquidcrystal 11. Alternatively, the mounting substrate 12 may be opticallyreflective or may have thereon an optically reflective coating so thatreflection by such reflective coating of incident light received throughthe protective coating 15 will be a function of whether or not there isan electric field applied across the encapsulated liquid crystal 11.

According to the preferred embodiment and best mode of the invention aplurality of encapsulated liquid crystals 11 would be applied to themounting substrate 12 in a manner such that the encapsulated liquidcrystals adhere to the mounting substrate 12 or to an interfacematerial, such as the electrode 13, for suppport by the mountingsubstrate 12 and retention in a fixed position relative to the otherencapsulated liquid crystals 11. Most preferably the encapsulatingmedium of which the capsule 22 is formed is also suitable for binding orotherwise adhering the capsule 22 to the substrate 12. Alternatively, afurther binding medium (not shown) may be used to adhere theencapsulated liquid crystals 11 to the substrate 12. Since the capsules22 are adhered to the substrate 12, and since each capsule 22 providesthe needed confinement for the liquid crystal material 20, a secondmounting substrate, such as the additional one shown in the prior artliquid crystal device 1 of FIG. 1, ordinarily would be unnecessary.However, for the purpose of providing protection from scarring,electrochemical deterioration, e.g. oxidation, or the like, of theelectrode 14, a protective coating 15 may be provided on the side orsurface of the liquid crystal device 10 opposite the mounting substrate12, the latter providing the desired physical protection on its own sideof the device 10.

Since the encapsulated liquid crystals 11 are relatively securelyadhered to the substrate 12 and since there ordinarily would be no needfor an additional substrate, as mentioned above, the electrode 14 may beapplied directly to the encapsulated liquid crystals 21.

Turning now to FIG. 3, an example of a liquid crystal device 10' inaccordance with the invention is shown in the form of a liquid crystaldisplay device, which appears as a square cornered figure eight 30 onthe substrate 12, which in this case preferably is of a plasticmaterial, such as Mylar, or may alternatively be another material, suchas glass, for example. The shaded area appearing in FIG. 3 to form thesquare cornered figure eight is formed of plural encapsulated liquidcrystals 11 arranged in one or more layers on and adhered to thesubstrate 12.

An enlarged fragmentary section view of a portion 32 of the figure eight30 and substrate 12 is illustrated in FIG. 4. As is seen in FIG. 4, onthe surface 31 of the substrate 12, which may be approximately 10 milsthick, is deposited a 200 angstrom thick electrode layer 33 of, forexample, indium tin oxide or other suitable electrode material such asgold, aluminum, tin oxide, antimony tin oxide, etc. One or more layers34 of plural encapsulated liquid crystals 11 are applied and adhereddirectly to the electrode layer 33. Such adherence according to thepreferred embodiment and best mode is effected by the encapsulatingmedium that forms respective capsules 22, although, if desired, as wasmentioned above, an additional adhering or binding material may be usedfor such adherence purposes. The thickness of the layer 34 may be, forexample, approximately 0.3 to 10 mils, preferably 0.7 to 4 mils, morepreferably 0.8 to 1.2 mils, especially 1 mil. Other thicknesses may alsobe used, depending inter alia on the ability to form a thin film and theelectrical breakdown properties of the film. A further electrode layer33 is deposited on the layer 34 either directly to the material of whichthe capsules 22 are formed or, alternatively, to the additional bindingmaterial used to bind the individual encapsulated liquid crystals 11 toeach other and to the mounting substrate 12. The electrode layer 35 maybe, for example, approximately 1/2 mil thick and may be formed, forexample, of electrically conductive ink or of the materials mentionedabove for layer 33. A protective coating layer 36 for the purposesdescribed above with respect to the coating 15 in FIG. 3 also may beprovided as is shown in FIG. 4.

In a conventional visual display device either of the liquid crystal orlight emitting diode type, the figure eight element 30 ordinarily wouldbe divided into seven electrically isolated segments, each of which maybe selectively energized or not so as to create various numeralcharacters. For example, energization of the segments 30a and 30b woulddisplay the numeral "1", and energization of the segments 30a, 30b, and30c would display the numeral "7".

A feature of the present invention utilizing the encapsulated liquidcrystals 11 is that a versatile substrate 12 can be created to becapable of displaying virtually any desired display as a function ofonly the selective segments of conductive ink electrodes printed on theliquid crystal material. In this case, the entire surface 31 of thesubstrate 12 may be coated with electrode material 33, and even theentire surface of that electrode material may be coated substantiallycontiguously with layer 34 of encapsulated liquid crystals 11.Thereafter, a prescribed pattern of electrode segments of conductive ink35 may be printed where desired on the layer 34. A single electricallead may attach the surface 31 to a voltage source, and respectiveelectrical leads may couple the respective conductive ink segments viarespective controlled switches to such voltage source. Alternatively,the encapsulated liquid crystals 11 and/or the electrode material 33 maybe applied to the surface 31 only at those areas where display segmentsare desired. The ability to apply encapsulated liquid crystal to only adesired area or plurality of areas such as the segments of a display byessentially conventional processes (such as e.g. silk-screening or otherprinting processes) is particularly attractive, when compared with theprior art, which has the problem of containing liquid crystals betweenflat plates.

Although a detailed description of the operation of the individualencapsulated liquid crystals 11 will be presented below, it will sufficehere to note that the encapsulated liquid crystals in the layer 34function to attenuate or not to attenuate light incident thereon independence on whether or not an electric field is applied thereacross.Preferably a pleochroic dye is present in solution in the liquid crystalmaterial to provide substantial attenuation by absortion in the"field-off" condition but to be substantially transparent in the"field-on" condition. Such an electric field may be, for example, oneproduced as a result of the coupling of the electrode layer portions 33,35 at an individual segment, such as segment 30a, of the liquid crystaldevice 10' to an electrical voltage source. The magnitude of theelectric field required to switch the encapsulated liquid crystals 11from a no field (deenergized) condition to a field-on (energized)condition may be a function of several parameters, including, forexample, the diameter of the individual capsules and the thickness ofthe layer 34, which in turn may depend on the diameter of individualcapsules 22 and the number of such capsules in the thickness directionof layer 34. Importantly, it will be appreciated that since the liquidcrystal material 20 is confined in respective capsules 22 and since theindividual encapsulated liquid crystals 11 are secured to the substrate12, the size of the liquid crystal device 10' or any other liquidcrystal device employing encapsulated liquid crystals in accordance withthe present invention is virtually unlimited. Of course, at those areaswhere it is intended to effect a change in the optical properties of theencapsulated liquid crystals of such a device in response to a no fieldor field on condition, it would be necessary to have at such areaselectrodes or other means for applying to such liquid crystals asuitable electric field.

The electrode layer 33 may be applied to the substrate 12 byevaporation, by vacuum deposition, by sputtering, by printing or byanother conventional technique. Moreover, the layer 34 of encapsulatedliquid crystals 11 may be applied, for example, by a web or gravureroller or by reverse roller printing techniques. The electrode layer 35also may be applied by various printing, stenciling or other techniques.If desired, the electrode layer 33 may be prepared as a full coating ofthe substrate 12, such as Mylar, as described above, as part of theprocess in which the Mylar sheet material is manufactured, and the layer34 also may be applied as part of such manufacturing process.

The ability to make and to use successfully liquid crystal devices ofthe type just described using encapsulated liquid crystals is due to theability to make encapsulated liquid crystals and to the properties ofsuch encapsulated liquid crystals, both of which are features of thepresent invention. These features now will be described with referenceto FIGS. 5, 6 and 7 in particular.

Referring specifically to FIG. 5, the capsule 22 has a generally smoothcurved interior wall surface 50 defining the boundary of the volume 21.The actual dimensional parameters of the wall surface 50 and of theoverall capsule 22 are related to the quantity of liquid crystalmaterial 20 contained therein. Additionally, the capsule 22 applies aforce to the liquid crystals 20 tending to pressurize or at least tomaintain substantially constant the pressure within the volume 21. As aresult of the foregoing, and due to the surface wetting nature of theliquid crystal, the structure which ordinarily in free form would tendto be straight, although perhaps randomly distributed, is distorted tocurve in a direction that generally is parallel to a relativelyproximate portion of the interior wall surface 50. Due to suchdistortion the liquid crystals store elastic energy. For simplicity ofillustration, and for facility of comprehending the foregoing concept, alayer 51 of liquid crystal molecules whose directional orientation isrepresented by respective dashed lines 52 is shown in closest proximityto the interior wall surface 50. The directional orientation of themolecules 52 is distorted to curve in the direction that is parallel toa proximate area of the wall surface 50. The directional pattern of theliquid crystal molecules away from the boundary layer 52 within thecapsule is represented by dashed lines 53. The liquid crystal moleculesare directionally represented in such layers, but it will be appreciatedthat the liquid crystal molecules themselves are not confined to suchlayers. Thus, the organization in an individual capsule is determined bythe organization of the structure 52 at the wall and is fixed unlessacted on by outside forces, e.g. an electric field. On removal of thefield, the directional orientation would revert back to the originalorientation such as that shown in FIG. 5.

In the preferred embodiment and best mode of the present invention theliquid crystal molecules 52 are of the nematic type. Such moleculesusually assume a parallel configuration, and a liquid crystal materialcomprised of such nematic molecules usually is optical polarizationdirection sensitive. However, since the structure 52 in the encapsulatedliquid crystal 11 is distorted or forced to assume a curved form in thefull three dimensions of the capsule 22, such nematic liquid crystalmaterial in such capsule takes on an improved characteristic of beinginsensitive to the direction of optical polarization of light incidentthereon. The inventor has discovered, moreover, that when the liquidcrystal material 20 in the capsule 22 has pleochroic dye dissolvedtherein, such dye, which ordinarily also would be expected to haveoptical polarization sensitivity, no longer is polarization sensitivebecause the dye tends to follow the same kind of curvature orientationor distortion as that of the liquid crystal structure.

It is noted here that the liquid crystal material 20 in the capsule 22has a discontinuity 55 in the generally spherical orientation thereof.Such discontinuity is caused by the inability of the liquid crystal toalign uniformly in a manner compatible with parallel alignment with thewall 54 and a requirement for minimum elastic energy. The liquid crystalwill, however, tend to follow around the discontinuity in the mannershown in planar form in FIG. 5, but in reality in three dimensions,following a pattern along the three dimensional generally sphericalinternal boundary wall surface 50 of the protruding discontinuity 55.Such discontinuity further distorts the liquid crystal structure whichin turn further decreases the possibility that the liquid crystalmaterial 20 would be sensitive to the optical polarization of theincident light.

With the liquid crystal structure being distorted to fold in on itselfgenerally in the manner illustrated in FIG. 5, the encapsulated liquidcrystal 11 ordinarily will absorb or block light from being transmittedtherethrough when no electric field is applied across the encapsulatedliquid crystal 11 and particularly across the liquid crystal material 20thereof.

Although the foregoing discussion has been in terms of a homogeueousorientation of the liquid crystal material (parallel to the capsulewall), such is not a requisite of the invention. All that is required isthat the interaction between the wall and the liquid crystal produce anorientation in the liquid crystal near that wall that is generallyuniform and piecewise continuous, so that the spatial averageorientation of the liquid crystal material over the capsule volume isstrongly curved and there is no substantial parallel directionalorientation of the liquid crystal in the absence of an electric field.It is this strongly curved orientation that results in theabsorption/scattering and polarization insensitivity in the field offcondition, which is a feature of this invention.

However, when an electric field is applied across the encapsulatedliquid crystal 11 in the manner illustrated in FIG. 6, the liquidcrystal and any pleochroic dye in solution therewith will align inresponse to the electric field in the manner shown in such figure. Suchalignment permits light to be transmitted through the encapsulatedliquid crystal 11, for example as described above with reference toFIGS. 2, 3 and 4.

In the field off condition, since the liquid crystal structure isdistorted to a curved form, the structure has a certain elastic energy.Such elastic energy causes the crytals to function to do things thatotherwise would not be possible when the liquid crystal structureassumes its ordinary linear form. For example, the discontinuityprotrusion 55 tends to cause scattering and absorption within thecapsule, and the tangential or parallel alignment of the liquid crystalmolecules to respective portions of interior wall surface 50 both causescattering and absorption within the capsule 22. On the other hand, whenthe electric field is applied in the manner illustrated in FIG. 6, notonly does the liquid crystal align as shown, but also the discontinuity55 tends to vanish, being dominated by the electric field. Accordingly,such discontinuity will have a minimum effect on optical transmissionwhen the encapsulated liquid crystal 11 is in a field on condition.

To optimize the contrast characteristics of a liquid crystal device,such as that shown at 10' in FIG. 3, comprised of encapsulated liquidcrystals 11, and more particularly, to avoid optical distortion, due torefraction of incident light passing from the encapsulating medium intothe liquid crystal material and vice versa, of the encapsulated liquidcrystal 11 of FIG. 6, the index of refraction of the encapsulatingmedium and that the ordinary index of refraction of the liquid crystalmaterial should be matched so as to be as much as possible the same. Thecloseness of the index matching will be dependent on the desired degreeof contrast and transparency in the device, but the ordinary index ofrefraction of the crystal and the index of the medium will preferablydiffer by no more than 0.03, more preferably 0.01, especially 0.001. Thetolerated difference will depend on capsule size and intended use of thedevice. The text "Optics" by Sears, published by Addison-Wesley,contains a thorough discussion of birefringence relevant to theforegoing, and the relevant portions of such text are incorporatedherein by reference.

However, when no field is applied there will be a difference in indicesof refraction at the boundary of the liquid crystal and capsule wall dueto the extraordinary index of refraction of the liquid crystal beinggreater than the encapsulating medium. This causes refraction at thatinterface or boundary and thus further scattering and is a reason whyencapsulated nematic liquid crystal material in accordance with thepresent invention, in particular, will function to prevent transissionof light even without the use of pleochroic dye.

Ordinarily the encapsulated liquid crystals 11 would be applied to thesubstrate 12 (FIG. 3) such that the individual encapsulated liquidcrystals 11 are relatively randomly oriented and preferably severalcapsules thick to assure an adequate quantity of liquid crystal materialon the surface 31 of the substrate to thereby provide the desired levelof light blockage and/or transmission characteristics for, for example,a liquid crystal device 10' or the like.

In a liquid crystal device, such as that shown in 10' in FIG. 3, whichis comprised of liquid crystal material 20 including pleochroic dye toform encapsulated liquid crystals 11 according to the invention, it hasbeen discovered that the degree of optical absorbency is at least aboutthe same as that of relatively free (unencapsulated) liquid crystalmaterial, including pleochroic dye such as that shown in FIG. 1. It alsohas been discovered unexpectedly that when the electric field is appliedin the manner illustrated in FIG. 6, for example, the clarity or lack ofopaqueness of the encapsulated liquid crystal material 20 includingpleochroic dye is at least about the same as that of the ordinary casein the prior art device 1 having dye in solution with relatively freeliquid crystal material.

It is important that electrical field E shown in FIG. 6 is applied tothe liquid crystal material 20 in the capsule 22 for the most partrather than being dissipated or dropped substantially in theencapsulating material of which the capsule itself is formed. In otherwords, it is important that there not be a substantial voltage dropacross or through the material of which the wall 54 of the capsule 22 isformed; rather, the voltage drop should occur predominantly across theliquid crystal material 20 within the volume 21 of the capsule 22.

The electrical impedance of the encapsulating medium preferably shouldin effect be sufficiently larger than that of the liquid crystalmaterial in the encapsulated liquid crystal 11 (FIG. 6) so that a shortcircuit will not occur exclusively through the wall 54, say from point Avia only the wall to point B, bypassing the liquid crystal material.Therefore, for example, the effective impedance to induced ordisplacement current flow through or via the wall 54 from point A onlyvia the wall 54 to point B, should be greater than the impedance thatwould be encountered in a path from point A to point A' inside theinterior wall surface 50, through the liquid crystal material 20 topoint B' still within the volume 21, thence ultimately to point B again.This condition will ensure that there will be a potential differencebetween point A and point B, which should be large enough to produce anelectric field across the liquid crystal material that will tend toalign it. It will be appreciated that due to geometrical considerations,namely the length through only the wall from point A to point B, forexample, that such a condition can still be met even though the actualimpedance of the wall material may be lower than that of the liquidcrystal material contained therein.

The dielectric constants (coefficients) of the material of which theencapsulating medium is formed and of which the liquid crystal materialis comprised and the effective capacitance values of the capsule wall54, particularly in a radial direction, and of the liquid crystalmaterial across which the electric field E is imposed should all be sorelated that the wall 54 of the capsule 22 does not substantiallydecrease the magnitude of the applied electric field E. Ideally thecapacitance dielectric constants of the entire layer 34 (FIG. 4) ofencapsulated liquid crystal material should be substantially the same inthe field-on condition.

A schematic electric circuit diagram representing the circuit acrosswhich the electric field E of FIG. 6 is imposed is illustrated in FIG.7. The electric field is derived from the voltage source 16 when theswitch 17 is closed. A capacitor 70 represents the capacitance of theliquid crystal material 20 in the encapsulated liquid crystal 11 whensuch electric field is applied in the manner illustrated in FIG. 6. Thecapacitor 71 represents the capacitance of the wall 54 of the capsule 22at an upper area (the direction conveniently referring to the drawingbut having no other particular meaning) and is, accordingly, curved in amanner similar to that of the upper portion of the capsule 22 of FIGS. 5and 6. The capacitor 72 similarly represents the capacitance of thelower portion of the capsule exposed to the electric field E. Themagnitudes of capacitance for each capacitor 70-72 will be a function ofthe dielectric constant (coefficient) of the material of which therespective capacitors are formed and of the spacing of the effectiveplates thereof. It is desirable that the voltage drop occurring acrossthe respective capacitors 71, 72 will be less than the voltage dropacross the capacitor 70; the result, then, is application of a maximumportion of the electric field E across the liquid crystal material 20 inthe encapsulated liquid crystal 11 for achieving optimized operation,i.e. alignment, of the liquid crystal molecules thereof with a minimumtotal energy requirement of the voltage source 16. However, it ispossible that the voltage drop in one or both capacitors 71, 72 willexceed the voltage drop across capacitor 70; this is operationallyacceptable as long as the drop across the capacitor 70 (liquid crystalmaterial) is great enough to produce an electric field that tends toalign the liquid crystal material to and/or toward the field-oncondition of FIG. 6, for example.

In connection with capacitor 71, for example, the dielectric material isthat of which the wall 54 is formed relatively near the upper portion ofthe capsule 22. The effective plates of such capacitor 71 are theexterior and interior wall surfaces 73, 51, and the same is true for thecapacitor 72 at the lower portion of the capsule 22 relative to theillustration of FIG. 6, for example. By making the wall 54 as thin aspossible, while still providing adequate strength for containment of theliquid crystal material 20 in the volume 21, the magnitudes ofcapacitors 71, 72 can be maximized, especially in comparison to therather thick or lengthy distance between the upper portion 74 of theliquid crystal material 20 of the lower portion 75 thereof whichapproximately or equivalently form the plates of the same number of thecapacitor 70.

The liquid crystal material 20 will have a dielectric constant valuethat is anisotropic. It is preferable that the dielectric constant(coefficient) of the wall 54 be no lower than the lower dielectricconstant (coefficient) of the anisotropic liquid crystal material 20 tohelp meet the above conditions. Since a typical lower dielectricconstant for liquid crystal material is about 6, this indicates that thedielectric constant of the encapsulating material is preferably at leastabout 6. Such value can vary widely depending on the liquid crystalmaterial used, being, for example, as low as about 3.5 and as high asabout 8 in the commonly used liquid crystals.

The encapsulated liquid crystal 11 has features such that since theliquid crystal structure is distorted and since the pleochroic dyesimilarly is distorted, absorbency or blockage of light transmissionthrough the encapsulated liquid crystals will be highly effective whenno electric field E is applied thereacross. On the other hand, due bothto the efficient application of an electric field across the liquidcrystal material 20 in the encapsulated liquid crystals 11 to align theliquid crystal molecules or structure and the dye along therewith aswell as the above described preferred index of refraction matching, i.e.of the encapsulating medium and of the liquid crystal material, so thatincident light will not be refracted or bent at the interface betweenthe capsule wall 54 and the liquid crystal material 20 when an electricfield is applied, the encapsulated liquid crystal 11 will have a goodoptically transmissive characteristic.

Since a plurality of encapsulated liquid crystals 11 ordinarily isrequired to construct a final liquid crystal device, such as the device10' of FIG. 3, and since those encapsulated liquid crystals areordinarily present in several layers, it is desirable for the liquidcrystal material to have a relatively high dielectric anisotropy inorder to reduce the voltage requirements for the electric field E. Morespecifically, the differential between the dielectric constant(coefficient) for the liquid crystal material 20 when no electric fieldis applied which constant (coefficient) should be rather small, and thedielectric constant (coefficient) for the liquid crystal material whenit is aligned upon application of an electric field, which constant(coefficient) should be relatively large, should be as large as possibleconsistent with the dielectric of the encapsulating medium.

The capsules 22 may be of various sizes. The smaller the capsule size,though, the higher the requirements will be for the electric field toeffect alignment of the liquid crystal molecules in the capsule. Also,when the capsule size is relatively small, more capsules are requiredper unit area of the layer 34, and, therefore, more electric voltagedrop losses will occur in the encapsulating medium than for larger sizecapsules, the density per unit area of which would be smaller. Accordingto a preferred embodiment and best mode of the present invention, adevice made with the encapsulated liquid crystals 11, such as the liquidcrystal device 10', should use capsules of uniform size so that thedevice 10' can be energized or deenergized in a relatively uniform andwell controlled manner. In contrast, when the capsules are of anon-uniform size, then non-uniform energization of the respectivecapsules, i.e. alignment of the liquid crystal molecules of each, wouldoccur upon application of the electric field. Ordinarily the capsules 22should have a size on the order of from about 1 to about 30 microns indiameter.

As was noted above, the larger the capsule size, the smaller theelectric field required to effect alignment of the liquid crystalmolecules therein. However, the larger the sphere, the longer theresponse time. A person of ordinary skill in the art should have nodifficulty, having regard to this disclosure, in determining a suitableor optimum capsule size for a given application.

Currently a preferred liquid crystal material is nematic material NM8250sold by American Liquid Xtal Chemical Corp., Kent, Ohio, U.S.A. and the40% material below. Other liquid crystal materials may be esters ormixtures thereof, biphenyls or mixtures thereof, and the like, such asE-7, E-11, E-63, ZLI-2344, and ZLI-2392, as supplied by E. MerckChemicals, Darmstadt, West Germany.

The encapsulating medium forming capsules 22 should be of a type that issubstantially completely unaffected by and does not react with orotherwise chemically affect the liquid crystal material. In particular,the liquid crystal material should not be soluble in the encapsulatingmedium or vice versa. The other characteristics described aboveconcerning dielectric constants (coefficients) and indices of refractionwith respect to the liquid crystal material and to the encapsulatingmedium also constrain material selection. Moreover, when a pleochroicdye is employed, the encapsulating medium also should be unaffected byand should not affect the dye material. On the other hand, the dyeshould be soluble in the liquid crystal material and not subject toabsorption by the encapsulating medium. Additionally, to achieve thedesired relatively high impedance for the encapsulating medium, suchmedium should have a relatively high level of purity. Especially whenthe encapsulating medium is prepared as an aqueous dispersion or byionic polymerization, etc., it is important that the level of ionic(conductive) impurities should be as low as possible.

Examples of pleochroic dyes that may suitably be used in theencapsulated liquid crystals 11 in accordance with the present inventionare indophenol blue, Sudan black B, Sudan 3, and Sudan 2, and D-37, D-43and D-85 by E. Merck identified above.

Various resins and/or polymers may be used as the encapsulating medium.

Several types of liquid crystal material useful according to theinvention include the following four recipes:

10% Material

Pentylphenylmethoxy Benzoate: 54 grams

Pentylphenylpentyloxy Benzoate: 36 grams

Cyanophenylpentyl Benzoate: 2.6 grams

Cyanophenylpentyl Benzoate: 3.9 grams

Cyanophenylpentyloxy Benzoate: 1.2 grams

Cyanophenylheptyloxy Benzoate: 1.1 grams

Cyanophenyloctyloxy Benzoate: 0.94 grams

Cyanophenylmethoxy Benzoate: 0.35 grams

20% Material

Pentylphenylmethoxy Benzoate: 48 grams

Pentylphenylpentyloxy Benzoate: 32 grams

Cyanophenylpentyl Benzoate: 5.17 grams

Cyanophenylheptyl Benzoate: 7.75 grams

Cyanophenylpentyloxy Benzoate: 2.35 grams

Cyanophenylheptyloxy Benzoate: 2.12 grams

Cyanophenyloctyloxy Benzoate: 1.88 grams

Cyanophenylmethoxy Benzoate: 0.705 grams

40% Material

Pentylphenylmethoxy Benzoate: 36 grams

Pentylphenylpentyloxy Benzoate: 24 grams

Cyanophenylpentyl Benzoate: 10.35 grams

cyanophenylheptyl Benzoate: 15.52 grams

Cyanophenylheptyloxy Benzoate: 4.7 grams

Cyanophenylheptyloxy Benzoate: 4.23 grams

Cyanophenylheptyloxy Benzoate: 3.76 grams

Cyanophenylmethoxy Benzoate: 1.41 grams

40% MOD

Pentylphenylmethoxy Benzoate: 36 grams

Pentylphenylpentyloxy Benzoate: 24 grams

Cyanophenylpentyl Benzoate: 16 grams

Cyanophenylheptyl Benzoate: 24 grams

However, an encapsulating medium according to a preferred embodiment andbest mode of the present invention when the encapsulation is performedby emulsification is polyvinyl alcohol (PVA), which has been found tohave the desired properties mentioned above, especially in relation tothe above described preferred liquid crystal and pleochroic dyematerial. Specifically, PVA has a good, relatively high, dielectricconstant and has an index of refraction that is relatively closelymatched to that of the preferred liquid crystal material.

To purify PVA, the same may be dissolved in water and washed out withalcohol using a precipitation technique. Other techniques also may beused for purifying PVA so that it will have minimum salt or othercontent that would reduce appreciably the electrical impedance thereof.The preferred purified PVA is Gelvatol sold by Monsanto. If PVA isproperly purified, as aforesaid, it will serve well as its ownemulsifier and as a wetting agent for facilitating the manufacture ofencapsulated liquid crystals according to this method which will bedescribed below. Other types of encapsulating medium may be, forexample, gelatin; Carbopole (a carboxy polymethylene polymer of B. F.Goodrich Chemical Corporation) Gantrez (polymethyl vinyl ether/maleicanhydride) of GAF Corporation, preferably reached with water to form theacid, the latter two being polyelectrolytes; and these media may be usedalone or in combination with other polymers, such as PVA.

Other examples and characteristics of several PVA materials are shown inTable I.

                                      TABLE I                                     __________________________________________________________________________                                               TEMPERATURE                        CONTAINMENT MEDIUM                         &                                  (PVA)          VISCOSITY                                                                            % HYDROLYZED                                                                            MOLECULAR Wgt.                                                                           % SOLUTIONS                        __________________________________________________________________________    20-30          4-6 CPS                                                                              88.7-85.5 10,000     4% at 20° C.                Gelvatol, by                                                                  Monsanto Company                                                              40-20          2.4-3                                                                             CPS                                                                                77-72.9 3,000      4% at 20° C.                Galvatol, by                                                                  Monsanto Company                                                              523            21-25  87-89     --         4% at 20° C.                Air Products and                                                              Chemicals, Inc.                                                               72-60          55-60   99-100   --         4% at 20° C.                Elvanol, by                                                                   DuPont Company                                                                405            2-4 CPS                                                                              80-82     --         4% at 20° C.                Poval, by                                                                     Kurashiki                                                                     __________________________________________________________________________

The wetting ability of the PVA with respect to the liquid crystalmaterial in the respective capsules 22, facilitates the preferredparallel alignment especially at the interior wall surface 50 in thefield off condition and changing to the aligned position of FIG. 6 whenan electric field is applied.

An emulsion method for making encapsulated liquid crystals 11 mayinclude mixing together the encapsulating medium, the liquid crystalmaterial (including, if used, the pleochroic dye material), and perhapsa carrier medium, such as water. Mixing may occur in a variety of mixerdevices, such as a blender, a colloid mill, which is most preferred, orthe like. What occurs during such mixing is the formation of an emulsionof the ingredients, which subsequently can be dried eliminating thecarrier medium, such as water, and satisfactorily curing theencapsulating medium, such as the PVA. Although the capsule 22 of eachthusly made encapsulated liquid crystal 11 may not be a perfect sphere,each capsule will be substantially spherical in configuration because asphere is the lowest free energy state of the individual droplets,globules or capsules of the emulsion, both when originally formed andafter drying and/or curing has occurred.

It is noted here briefly that the characteristic of the pleochroic dyethat it must be soluble in the liquid crystal material and that it notbe subject to absorption by the water phase or polymer phase assuresthat such pleochroic dye will not be absorbed by the PVA or otherencapsulating medium or by the carrier medium, such as the water, usedduring the manufacturing process for the encapsulated liquid crystals11.

EXAMPLE 1

A 0.45% Sudan black B pleochroic dye was dissolved in a liquid crystalwhich was composed of aromatic esters. Such combined material iscommercially sold under the designation NM8250 by American Liquid XtalChemical Corp. of Kent, Ohio. Such material was mixed with a solution of7% PVA, which had been purified to remove all salts. The solution alsowas made with ASTM-100 water. The resulting mixture was put into acolloid mill whose conegap setting was 4 mils, and the material wasmilled for four minutes to give a rather uniform particle suspensionsize. The result was a stable emulsion whose suspended particle size wasapproximately 3 microns. The emulsion was cast on a Mylar film which wasprecoated with a 200 ohm per square layer of indium tin oxide electrodepurchased from Sierracin. A doctor blade was used to cast the emulsionmaterial on the Mylar film on the electrode coated side.

A 7 mil lay-down of the emulsion material was placed on such electrodeand was allowed to dry to a total thickness of 0.8 mil. A second layerof such emulsion subsequently was laid on the first with a resultingaggregate layer of liquid crystal droplets in a polyvinyl alcohol matrixhaving a thickness of 1.6 mil. Preferably the encapsulated liquidcrystals may be laid down in a single layer one or plural capsulesthick.

The thusly formed liquid crystal device, including the layer of Mylar,electrode, and encapsulated liquid crystals was then tested by applyingan electric field, whereupon the material changed from black to nearlyclear-transparent. The material exhibited a very wide viewing angle,i.e. the angle at which light was transmitted, and the contrast ratiowas 7:1 at 50 volts of applied electric field. The switching speed wasabout two milliseconds on and about 4 milliseconds off.

EXAMPLE 2

900 grams of 7% high viscosity fully hydrolysed polymer (SA-72 ofAmerican Liquid Xtal Chemical Corp.), 100 grams of 8250 nematic liquidcrystal material also of American Liquid Xtal Chemical Corp., 0.45 gramsof C26510 Sudan Black B, and 0.15 grams of C26100 Sudan III (the lattertwo ingredients being pleochroic dyes), were used. The polymer wasweighed out in a breaker. The liquid crystal was weighed out, was placedon a hot plate, and was heated slowly. The dye was weighted out on abalance and was added very slowly to the liquid crystal, being stirreduntil all the dye went into solution.

The liquid crystal and dye solution then was filtered through a standardMillipore filtering system using 8 ml. filter paper. The filtered liquidcrystal and dye solution was stirred into the polymer using a Teflonrod. Such mixture was encapsulated by placing the same in a colloid millthat was operated at medium shear for five minutes. The emulsion filmwas then pulled on a conductive polyester sheet.

In operation of such example, upon the application of a 10 volt electricfield, the liquid crystal structure began to align, and at 40 voltsreached saturation and maximum optical transmissivity.

EXAMPLE 3

The procedure of Example 2 was carried out using the same ingredientsand steps except that a 5% high viscosity fully hydrolysed polymer, suchas SA-72, was substituted for the 7% polymer of Example 2. Operationalresults were the same as in Example 2.

EXAMPLE 4

The process of Example 2 was carried out to make an emulsion using 4grams of 20% medium viscosity, partly hydrolysed polymer (such as 405identified in Table I above), 2 grams of 8250 nematic liquid crystalmaterial having 0.08 gm of D-37 magenta pleochroic dye (a proprietarypleochroic dye manufactured and/or sold by E. Merck of West Germany) inthe solution with the liquid crystal.

A slide was taken using a Teflon rod, and upon inspection showed mediumsize capsules of about 3 to 4 microns in diameter. The material wasfiltered through a Millipore screen filter and another slide was taken;on inspection there was very little change in capsule size from thefirst-mentioned inspection.

The emulsion was pulled onto a conductive polyester support film as inExample 2 using a doctor blade set at a 5 mil gap. In operation, theencapsulated liquid crystal material began to align upon the applicationof an electric field of 10 volts and was at saturation or full on atfrom about 40 to 60 volts.

EXAMPLE 5

Using a glass rod cleaned and washed with deionized ASTM-100 water, 2grams of 40% 8250 nematic liquid crystal material with 0.08 gm of D-37pleochroic dye dissolved therein was stirred into 4 grams of 405desalted 20% by weight medium hydrolysis medium viscosity polymer verycarefully for approximately 15 minutes. The material was then placedthrough a Millipore screen filter approximately 4 microns in size. Aslide was taken after the bubbles had dissipated.

Thereafter, a film was pulled at a gap 5 mil setting on Intrexelectrically conductive electrode film material that was placed on apolyester support of Mylar material. In operation it was evident thatthe liquid crystal material began aligning upon application of a 5 voltelectric field. Contrast was good and the liquid crystal material was atfull on or saturation upon the application of a 40 volt electric field.

EXAMPLE 6

This example used 8 grams of D-85 pleochroic dye dissolved in E-63biphenyl liquid crystal. Such material is sold premixed by British DrugHouse, which is a subsidiary of E.Merck of West Germany. The examplealso used 16 grams of 20% PVA medium viscosity medium hydrolysis polymeras the encapsulating medium. The liquid crystal and pleochroic dyesolution was mixed carefully by hand into the polymer at a slow rate.The combined material was then screened at a low shear. A slide wastaken and on observation showed approximately 3 micron size capsules. Afilm of such emulsion was pulled onto an electrically conductivepolyester sheet, as above, using a gap 5 mil setting. The film was on orbegan having liquid crystal structure align with the electric field atapproximately 6 volts and was at saturation or full on at 24 volts.

EXAMPLE 7

A mixture was formed of 8250 nematic liquid crystal with 0.08 gm D-37pleochroic dye in solution therewith and a solution of 15% AN169 Gantrexin 85% water. The mixture was of 15% liquid crystal and 85% Gantrex asthe containment medium. The mixture was homogenized at low shear to forman emulsion, which was applied to an electrode/support film as above;such support film was about 1.2 mils thick. After drying of theemulsion, the resulting liquid crystal emulsion responded to an electricfield generally as above, substantially absorbing or at least notsubstantially transmitting light when in field-off condition, showing athreshold of about 7 volts to begin transmitting, and having asaturation level of substantially maximum transmission at about 45volts.

In accordance with the present invention the quantities of ingredientsfor making the encapsulated liquid crystals 11, for example in themanner described above, may be, as follows:

The liquid crystal material--This material may be from about 5% to about20% and preferably about 50% (and in some circumstances even greaterdepending on the nature of the encapsulating aterial) including thepleochroic dye, by 25% (when using Gelvatol as the encapsulatingmaterial) volume of the total solution delivered to the mixingapparatus, such as a colloid mill. The actual amount of liquid crystalmaterial used should ordinarily exceed the volume quantity ofencapsulating medium, e.g. PVA to optimize the capsule size.

The PVA--The quantity of PVA in the solution should be on the order offrom about 5% to about 50%, and possibly even greater depending on thehydrolysis and molecular weight of the PVA, and preferably, as describedabove, about 22%, For example, if the PVA has too large a molecularweight, the resulting material will be like glass, especially if toomuch PVA is used in the solution. On the other hand, if the molecularweight is too low, use of too little PVA will result in too low aviscosity of the material, and the resulting emulsion will not hold upwell, nor will the droplets of the emulsion solidify adequately to thedesired spherical encapsulated liquid crystals.

Carrier medium--The remainder of the solution would be water or other,preferably volatile, carrier medium, as described above, with which theemulsion can be made and the material laid down appropriately on asubstrate, electrode or the like.

It will be appreciated that since the uncured capsules or droplets ofencapsulating medium and liquid crystal material are carried in aliquid, various conventional or other techniques may be employed tograde the capsules according to size so that the capsules can bereformed if of an undesirable size by feeding again through the mixingapparatus, for example, and so that the finally used capsules will be ofa desired uniformity for the reasons expressed above.

Although the encapsulation technique has been described in detail withreference to emulsification, since the fact that the encapsulantmaterial and binder are the same makes facile the production of liquidcrystal devices; the preparation of discrete capsules of the liquidcrystal material may on occasion be advantageous, and the use of suchdiscrete capsules (with a binder) is within the contemplated scope ofthis invention.

Although the presently preferred invention operates in response toapplication and removal of an electric field, operation also may beeffected by application and removal of a magnetic field.

I claim:
 1. A billboard display comprising a liquid crystal apparatus,including operationally nematic liquid crystal material and containmentmeans having a curvilinear surface for inducing a generally non-parallelalignment of said liquid crystal material which in response to suchalignment at least one of scatters and absorbs light and which inresponse to a prescribed input reduces the amount of such scattering orabsorption.
 2. The invention of claim 1, said liquid crystal apparatusbeing over a substantial surface area of the billboard.
 3. The inventionof claim 2, further comprising pleochroic dye mixed with said liquidcrystal material.
 4. The invention of claim 2, wherein the invention isoperative independent of polarization of light incident thereon.
 5. Theinvention of claim 2, wherein said prescribed input is an AC electricalfield or a DC electrical field.
 6. Liquid crystal apparatus, comprisingoperationally nematic liquid crystal material, a non-planar containmentmeans for inducing a generally non-parallel alignment of said liquidcrystal materail which in response to such alignment at least one ofscatters and absorbs light and which in response to a prescribed inputreduces the amount of such scattering or absorption, and electrode meansfor applying an electric field as such prescribed input, said electrodemeans comprising electrically conductive ink.
 7. The invention of claim6, said electrically conductive ink being applied to a surface of saidcontainment means.
 8. The invention of claim 6, said electricallyconductive ink being optically reflective.
 9. The invention of claim 6,further comprising substrate means for supporting said liquid crystalmaterial in said containment means, said electrically conductive inkbeing applied to a surface of said containment means remote from saidsubstrate means.
 10. The invention of claim 9, further comprisingfurther electrode means on said substrate means, both said electrodemeans being positioned and coupled to apply such electric field inresponse to receiving an electrical input.
 11. The invention of claim10, wherein said further electrode is applied over substantially theentire surface of said substrate means that is directly supporting saidliquid crystal material and containment means, and said electricallyconductive ink electrode is arranged in a pattern over a portion lessthan all of such surface of said containment means.
 12. The invention ofclaim 6, further comprising pleochroic dye mixed with said liquidcrystal material.
 13. The invention of claim 6, wherein the invention isoperative independent of polarization of light incident thereon.
 14. Theinvention of claim 10, wherein said prescribed input is an AC electricalfield or a DC electrical field.
 15. Liquid crystal apparatus, comprisingoperationally nematic liquid crystal material, non-parallel containmentmeans for inducing a generally non-parallel alignment of said liquidcrystal material which in response to such alignment at least one ofscatters and absorbs light and which in response to a prescribed inputreduces the amount of such scattering or absorption, and electrode meansfor applying an electric field as such prescribed input, said electrodemeans being applied by at least one of evaporation, vacuum deposition,sputtering, printing, web roller, gravure roller, reverse rollerprinting, stencilling, or printing.
 16. The invention of claim 15,further comprising substrate means for supporting said liquid crystalmaterial in said containment means, and said liquid crystal material andsaid containment means being applied to sid substrate means bysilk-screening.
 17. The invention of claim 15, further comprisingpleochroic dye mixed with said liquid crystal material.
 18. Liquidcrystal apparatus, comprising operationally nematic liquid crystalmaterial, containment means for containing said liquid crystal material,said containment means having a curvilinear surface means for inducing agenerally non-parallel alignment of said liquid crystal material whichin response to such alignment at least one of scatters and absorbs lightand which is response to a prescribed input reduces the amount of suchscattering or absorption, and substrate means for supporting said liquidcrystal material in said containment means, said substrate includingreflecting means for reflecting light transmitted through said liquidcrystal material in the presence of such prescribed input.
 19. Theinvention of claim 18, said reflecting means comprising a reflectivecoating on said substrate means.
 20. The invention of claim 18, saidsubstrate means being selected from the group consisting of Mylar andglass.
 21. The invention of claim 18, further comprising pleochroic dyemixed with said liquid crystal material.
 22. The invention of claim 18,wherein the invention is operative independent of polarization of lightincident thereon.
 23. Liquid crystal apparatus, comprising operationallynematic liquid crystal material, curvilinear containment means forinducing a generally non-parallel alignment of said liquid crystalmaterial which in response to such alignment at least one of scattersand absorbs light and which in response to a prescribed input reducesthe amount of such scattering or absorption, and substrate means forsupporting theron said containment means and liquid crystal material,said containment means having a surface remote from said substratemeans, said surface being substantially directly unsupported or coveredby a separate substrate means.
 24. The invention of claim 23, furthercomprising electrode means at said surface for applying an electricfield to said liquid crystal material as such prescribed input.
 25. Theinvention of claim 24, said electrode means being applied by at leastone of evaporation, vacuum deposition, sputtering, printing, web rollerprinting, gravure roller printing, reverse roller printing, andstenciling.
 26. The invention of claim 24, said electrode meanscomprising electrically conductive ink.
 27. The invention of claim 24,further comprising further electrode means on said substrate means, bothsaid electrode means being positioned and coupled to apply such electricfield in response to receiving an electrical input.
 28. The invention ofclaim 27, wherein said further electrode is applied over substantiallythe entire surface of said substrate means that is directly supportingsaid liquid crystal material and containment means.
 29. The invention ofclaim 28, said electrode means at said surface being arranged in apattern over less than all of said surface.
 30. The invention of claim29, said electrode means at said surface comprising electricallyconductive ink printed on said surface in a predetermined pattern. 31.The invention of claim 23, said substrate means including reflectingmeans for reflecting light transmitted through said liquid crystalmaterial in the presence of such prescribed input.
 32. The invention ofclaim 31, said reflecting means comprising a reflective coating on saidsubstrate means.
 33. The invention of claim 23, wherein said substratemeans comprises at least one component of the group consisting of Mylarand glass.
 34. The invention of claim 23, further comprising pleochroicdye mixed with said liquid crystal material.
 35. The invention of claim23, wherein the invention is operative independent of polarization oflight incident thereon.
 36. The invention of claim 27, wherein saidprescribed input is an AC electrical field or a DC electrical field. 37.Liquid crystal apparatus, comprising a substrate and supported by saidsubstrate a layer of operationally nematic liquid crystal material andcontainment means having a curvilinear surface for inducing a generallynon-parallel alignment of said liquid crystal material which in responseto such alignment at least one of scatters and absorbs light and whichin response to a prescribed input reduces the amount of such scatteringor absorption, said layer being from about 0.3 mil to about 10 milsthick.
 38. The invention of claim 37, said layer being from about 0.7mil to about 4 mils thick.
 39. The invention of claim 37, said layerbeing from about 0.8 mil to about 1.2 mils thick.
 40. The invention ofclaim 37, further comprising an electrode between said substrate andsaid layer of liquid crystal material and containment means.
 41. Theinvention of claim 40, said electrode being about 200 Angstroms thick.42. The invention of claim 40, said electrode comprising at least onecomponent of the group consisting of indium tin oxide, gold, aluminum,tin oxide, and antimony tin oxide.
 43. The invention of claim 40,further comprising a further electrode at an opposite surface of saidlayer away from said substrate.
 44. The invention of claim 43, saidfurther electrode comprising electrically conductive ink.
 45. Theinvention of claim 37, said substrate being about 10 mils thick.
 46. Theinvention of claim 37, said liquid crystal material and containmentmeans comprising capsule-like volumes of liquid crystal material, andsaid layer comprising plural layers of said capsule-like volumes thick.47. The invention of claim 37, said liquid crystal material comprisingoptically anisotropic liquid crystal material, and wherein thedifference between the ordinary index of refraction of said liquidcrystal material and the index of refraction of said containment meansbeing no greater than 0.3.
 48. The invention of claim 37, said liquidcrystal material having positive dielectric anisotropy, and wherein thelower dielectric constant of said liquid crystal material is betweenabout 3.5 and about
 8. 49. The invention of claim 37, wherein saidcontainment means comprises at least one component of the groupconsisting of gelatin, polyvinyl alcohol, carboxy polymethylene polymerand polymethyl vinyl ether/maleic anhydride.
 50. The invention of claim37, further comprising pleochroic dye mixed with said liquid crystalmaterial.
 51. The invention of claim 37, wherein the invention isoperative independent of polarization of light incident thereon.
 52. Theinvention of claim 37, wherein said prescribed input is an AC electricalfield or a DC electrical field.
 53. A base stock liquid crystalapparatus, comprising a support substrate, and supported with respect tosaid substrate at least one layer of operationally nematic liquidcrystal material and containment means having a curvilinear surface forinducing a generally non-parallel alignment of said liquid crystalmaterial which in response to such alignment at least one of scattersand absorbs light and which in response to a prescribed input reducesthe amount of such scattering or absorption.
 54. The invention of claim53, further comprising a first electrode between said substrate and saidlayer of liquid crystal material and containment means.
 55. Theinvention of claim 54, said electrode being over substantially theentire area of said substrate where said layer is supported on saidsubstrate.
 56. The invention of claim 55, further comprising a furtherelectrode applied to at least part of said layer to cooperate with saidfirst mentioned electrode to apply an electric field to selected areasof said liquid crystal material as such prescribed input.
 57. Theinvention of claim 53, further comprising pleochroic dye mixed with saidliquid crystal material.
 58. The invention of claim 53, wherein theinvention is operative independent of polarization of light incidentthereon.
 59. The invention of claim 55, wherein said prescribed input isan AC electrical field or a DC electrical field.
 60. The invention ofclaim 1, wherein said curvilinear surface comprises a wall of a curvedvolume formed of said containment means and in which said liquid crystalmaterial is contained, said wall inducing a non-parallel distortedalignment of the liquid crystal structure when in the absence of anelectric field.
 61. The invention of claim 60, wherein said liquidcrystal material has positive dielectric anisotropy.
 62. The inventionof claim 61, wherein said liquid crystal material has an ordinary indexof refraction substantially matched to the index of refraction of saidcontainment means to maximize light transmission in the presence of anelectric field.
 63. The invention of claim 62, wherein said liquidcrystal material has an extraordinary index of refraction different fromthe index of refraction of said containment means to cause refractionand scattering of light in the absence of an electric field.
 64. Theinvention of claim 62, further comprising pleochroic dye mixed with saidliquid crystal material, said liquid crystal material and pleochroic dyebeing operative to absorb light in the absence of an electric field andbeing responsive to an electric field to reduce the amount of lightabsorption and to increase light transmission thereby.
 65. The inventionof claim 6, wherein said non-planar containment means comprises a wallof a curved volume formed of said containment means and in which saidliquid crystal material is contained, said wall being operative todistort the structure of said liquid crystal material to a non-parallelalignment when in the absence of an electric field.
 66. The invention ofclaim 65, wherein said liquid crystal material has positive dielectricanisotropy.
 67. The invention of claim 66, wherein said liquid crystalmaterial has an ordinary index of refraction substantially matched tothe index of refraction of said containment means to maximize lighttransmission in the presence of an electric field.
 68. The invention ofclaim 67, wherein said liquid crystal material has an extraordinaryindex of refraction different from the index of refraction of saidcontainment means to cause refraction and scattering of light in theabsence of an electric field.
 69. The invention of claim 67, furthercomprising pleochroic dye mixed with said liquid crystal material, saidliquid crystal material and pleochroic dye being operative to absorblight in the absence of an electric field and being responsive to anelectric field to reduce the amount of light absorption and to increaselight transmission thereby.
 70. The invention of claim 15, wherein saidnon-parallel containment means comprises a curved wall of a curvedvolume formed of said containment means and in which said liquid crystalmaterial is contained, said wall being operative to distort the liquidcrystal structure to non-parallel alignment when in the absence of anelectric field.
 71. The invention of claim 70, wherein said liquidcrystal material has positive dielectric anisotropy.
 72. The inventionof claim 71, wherein said liquid crystal material has an ordinary indexof refraction substantially matched to the index of refraction of saidcontainment means to maximize light transmission in the presence of anelectric field.
 73. The invention of claim 72, wherein said liquidcrystal material has an extraordinary index of refraction different fromthe index of refraction of said containment means to cause refractionand scattering of light in the absence of an electric field.
 74. Theinvention of claim 72, further comprising pleochroic dye mixed with saidliquid crystal material, said liquid crystal material and pleochroic dyebeing operative to absorb light in the absence of an electric field andbeing responsive to an electric field to reduce the amount of lightabsorption and to increase light transmission thereby.
 75. The inventionof claim 18, wherein said curvilinear surface means comprises a wall ofa curved volume formed of said containment means and in which saidliquid crystal material is contained, said wall inducing a non-paralleldistorted alignment of the liquid crystal structure when in the absenceof an electric field.
 76. The invention of claim 75, wherein said liquidcrystal material has positive dielectric anisotropy.
 77. The inventionof claim 76, wherein said liquid crystal material has an ordinary indexof refraction substantially matched to the index of refraction of saidcontainment means to maximize light transmission in the presence of anelectric field.
 78. The invention of claim 77, wherein said liquidcrystal material has an extraordinary index of refraction different fromthe index of refraction of said containment means to cause refractionand scattering of light in the absence of an electric field.
 79. Theinvention of claim 77, further comprising pleochroic dye mixed with saidliquid crystal material, said liquid crystal material and pleochroic dyebeing operative to absorb light in the absence of an electric field andbeing responsive to an electric field to reduce the amount of lightabsorption and to increase light transmission thereby.
 80. The inventionof claim 23, wherein said curvilinear containment means includes a wallof a curved volume formed of said containment means and in which saidliquid crystal material is contained, said wall inducing a non-paralleldistorted alignment of the liquid crystal structure when in the absenceof an electric field.
 81. The invention of claim 80, wherein said liquidcrystal material has positive dielectric anisotropy.
 82. The inventionof claim 81, wherein said liquid crystal material has an ordinary indexof refraction substantially matched to the index of refraction of saidcontainment means to maximize light transmission in the presence of anelectric field.
 83. The invention of claim 82, wherein said liquidcrystal material has an extraordinary index of refraction different fromthe index of refraction of said containment means to cause refractionand scattering of light in the absence of an electric field.
 84. Theinvention of claim 82, further comprising pleochroic dye mixed with saidliquid crystal material, said liquid crystal material and pleochroic dyebeing operative to absorb light in the absence of an electric field andbeing responsive to an electric field to reduce the amount of lightabsorption and to increase light transmission thereby.
 85. The inventionof claim 37, wherein said curvilinear surface comprises a wall of acurved volume formed of said containment means and in which said liquidcrystal material is contained, said wall inducing a non-paralleldistorted alignment of the liquid crystal structure when in the absenceof an electric field.
 86. The invention of claim 85, wherein said liquidcrystal material has positive dielectric anisotropy.
 87. The inventionof claim 86, wherein said liquid crystal material has an ordinary indexof refraction substantially matched to the index of refraction of saidcontainment means to maximize light transmission in the presence of anelectric field.
 88. The invention of claim 87, wherein said liquidcrystal material has an extraordinary index of refraction different fromthe index of refraction of said containment means to cause refractionand scattering of light in the absence of an electric field.
 89. Theinvention of claim 87, further comprising pleochroic dye mixed with saidliquid crystal material, said liquid crystal material and pleochroic dyebeing operative to absorb light in the absence of an electric field andbeing responsive to an electric field to reduce the amount of lightabsorption and to increase light transmission thereby.
 90. The inventionof claim 53, wherein said curvilinear surface comprises a wall of acurved volume formed of said containment means and in which said liquidcrystal material is contained, said wall inducing a non-paralleldistorted alignment of the liquid crystal structure when in the absenceof an electric field.
 91. The invention of claim 90, wherein said liquidcrystal material has positive dielectric anisotropy.
 92. The inventionof claim 91, wherein said liquid crystal material has an ordinary indexof refraction substantially matched to the index of refraction of saidcontainment means to maximize light transmission in the presence of anelectric field.
 93. The invention of claim 92, wherein said liquidcrystal material has an extraordinary index of refraction different fromthe index of refraction of said containment means to cause refractionand scattering of light in the absence of an electric field.
 94. Theinvention of claim 92, further comprising pleochroic dye mixed with saidliquid crystal material, said liquid crystal material and pleochroic dyebeing operative to absorb light in the absence of an electric field andbeing responsive to an electric field to reduce the amount of lightabsorption and to increase light transmission thereby.